Early tumor detection and treatment selection is paramount to achieving therapeutic success and long-term survival rates. At its early stage, many cancers are localized and can be treated surgically. However, well-defined tumor margins are often difficult to visualize with current imaging techniques. This has led to a disproportionate number of invasive biopsies. Highly-specific, molecular-targeted probes are needed for the early detection of molecular differences between normal and tumor cells, such as cancer-specific alterations in receptor expression levels. When combined with high-resolution imaging techniques, specific molecular-targeted probes will greatly improve detection sensitivity, facilitating characterization, monitoring and treatment of cancer.
Current fluorescence imaging probes typically consist of single conventional fluorophore (e.g., organic dyes, fluorescent proteins), fluorescent proteins (e.g., GFP) and semiconductor quantum dots (Q-dots). Single fluorophores are usually not stable and have limited brightness for imaging. Similar to dyes, the fluorescent proteins tend to exhibit excited state interactions which can lead to stochastic blinking, quenching and photobleaching. Q-dots are generally made from heavy metal ions such as Pb2+ or Cd2+ and, therefore, are toxic. Burns et al. “Fluorescent core-shell silica nanoparticles: towards “Lab on a Particle” architectures for nanobiotechnology”, Chem. Soc. Rev., 2006, 35, 1028-1042.
Fluorescent nanoparticles having an electrically conducting shell and a silica core are known and have utility in modulated delivery of a therapeutic agent. U.S. Pat. Nos. 6,344,272, and 6,428,811. A shortcoming of existing fluorescent nanoparticles is their limited brightness and their low detectability as fluorescent probes in dispersed systems.
The present multifunctional fluorescent silica-based nanoparticles offer many advantages over other fluorescent probes. The nanoparticles are non-toxic, and have excellent photophysical properties (including fluorescent efficiency and photostability), high biocompatibility, and unique pharmacokinetics for molecular diagnostics and therapeutics. The nanoparticles are relatively small in size, and have a surface PEG coating that offers excellent renal clearance. The fluorescent nanoparticles of the present invention contain a fluorescent core and silica shell. The core-shell architectures, the great surface area and diverse surface chemistry of the nanoparticle permit multiple functionalities simultaneously delivered to a target cell. For example, the nanoparticle can be functionalized with targeting moieties, contrast agents for medical imaging, therapeutic agents, or other agents. The targeting moieties on the surface of the nanoparticle may be tumor ligands, which, when combined with nanoparticle-conjugated therapeutic agents, makes the nanoparticle an ideal vehicle for targeting and potentially treating cancer. Webster et al. Optical calcium sensors: development of a generic method for their introduction to the cell using conjugated cell penetrating peptides. Analyst, 2005; 130:163-70. The silica-based nanoparticle may be labeled with contrast agents for PET, SPECT, CT, MRI, and optical imaging.